Preheating of chemical vapor deposition precursors

ABSTRACT

Chemical vapor deposition methods utilizing preheating of one or more of the reactant gases used to form deposited layers, chemical vapor deposition systems to perform the methods, and apparatus containing deposited layers produced using the methods. The reactant gases contain at least one chemical vapor deposition precursor. Heating one or more of the reactant gases prior to introduction to the reaction chamber may be used to improve physical characteristics of the resulting deposited layer, to improve the physical characteristics of the underlying substrate and/or to improve the thermal budget available for subsequent processing. One example includes the formation of a titanium nitride layer with reactant gases containing the precursors of titanium tetrachloride and ammonia. Preheating the reactant gases containing titanium tetrachloride and ammonia can reduce ammonium chloride levels in the resulting titanium nitride layer, thereby reducing or eliminating the need for post-processing to remove the ammonium chloride impurity. Chemical vapor deposition systems include one or more heaters to raise the temperature of the reactant gases prior to introduction to the reaction chamber.

TECHNICAL FIELD

The present invention relates generally to chemical vapor deposition,and in particular to methods for chemical vapor deposition includingpreheating of the chemical vapor deposition precursors, systems toperform the methods, and apparatus produced by such methods.

BACKGROUND

Semiconductor integrated circuits (ICs) contain individual devices thatare typically coupled together using metal line interconnects andvarious contacts. In many applications, the metal lines are formed on adifferent level than the devices, separated by an intermetal dielectric,such as silicon oxide or borophosphosilicate glass (BPSG). Commonly usedmetal lines include aluminum, tungsten and copper, as well ascombinations of these materials with refractory metals and silicon.Interconnects used to electrically couple devices and metal lines areformed between the individual devices and the metal lines. A typicalinterconnect is composed of a contact hole (i.e. opening) formed in anintermetal dielectric layer over an active device region. The contacthole is often filled with a metal, such as aluminum or tungsten.

Interconnects often further contain a diffusion barrier layer sandwichedbetween the interconnect metal and the active device region at thebottom of the contact hole. Such layers prevent intermixing of the metaland the material from the active device region, such as silicon.Reducing intermixing generally extends the life of the device. Passivetitanium nitride (TiN) layers are commonly used as diffusion barrierlayers. An example may include the use of titanium nitride interposedbetween a silicide contact and a metal fill within a contact hole.Further uses of diffusion barrier layers may include a barrier layerinterposed between a polysilicon layer and a metal layer in a gate stackof a field effect transistor.

Titanium nitride is a desirable barrier layer because it is animpermeable barrier for silicon, and because it presents a high barrierto the diffusion of other impurities. Titanium nitride has relativelyhigh chemical and thermodynamic stability and a relatively lowresistivity. Titanium nitride layers are also often used as adhesionlayers, such as for tungsten films. While titanium nitride can be formedon the substrate by physical vapor deposition (PVD) or chemical vapordeposition (CVD) techniques, CVD is often the technique of choice.

CVD is a process in which a deposition surface is contacted with vaporsof volatile chemical compounds, generally at elevated temperatures. Thecompounds, or CVD precursors, are reduced or dissociated at thedeposition surface, resulting in an adherent coating of a preselectedcomposition. In contrast to physical deposition, CVD does not requirehigh vacuum systems and permits a wide variety of processingenvironments, including low pressure through atmospheric pressure, andis an accepted method for depositing homogeneous films over large areasand on non-planar surfaces.

CVD is often classified into various types in accordance with theheating method, gas pressure, and/or chemical reaction. For example,conventional CVD methods include cold-wall CVD, in which only adeposition substrate is heated; hot-wall CVD, in which an entirereaction chamber is heated; atmospheric CVD, in which reaction occurs ata pressure of about one atmosphere; low-pressure CVD (LPCVD) in whichreaction occurs at pressures from about 10⁻¹ to 100 torr; andplasma-assisted CVD (PACVD) and photo-assisted CVD in which the energyfrom a plasma or a light source activates the precursor to allowdepositions at reduced substrate temperatures. Other classifications areknown in the art.

In a typical CVD process, the substrate on which deposition is to occuris placed in a reaction chamber, and is heated to a temperaturesufficient to drive the desired reaction. The reactant gases containingthe CVD precursors are introduced into the reaction chamber where theprecursors are transported to, and subsequently adsorbed on, thedeposition surface. Surface reactions deposit nonvolatile reactionproducts on the deposition surface. Volatile reaction products are thenevacuated or exhausted from the reaction chamber. While it is generallytrue that the nonvolatile reaction products are deposited on thedeposition surface, and that volatile reaction products are removed, therealities of industrial processing recognize that undesirable volatilereaction products, as well as nonvolatile reaction products fromsecondary or side reactions, may be incorporated into the depositedlayer. Integrated circuit fabrication generally includes the depositionof a variety of material layers on a substrate, and CVD may used todeposit one or more of these layers.

As an example, one LPCVD process combines titanium tetrachloride (TiCl₄)and ammonia (NH₃) to deposit titanium nitride. However, LPCVD titaniumnitride using these precursors has a tendency to incorporate a largeamount of residual ammonium chloride in the film. This residual ammoniumchloride detrimentally effects the resistivity and barrier properties ofthe titanium nitride layer. Once exposed to air, the residual ammoniumchloride will cause the titanium nitride layer to absorb water and toform particles, both undesirable effects. It is known that residualammonium chloride can be reduced by the use of ammonia post-flow, orannealing in an ammonia atmosphere, subsequent to deposition. However,such post-processing leads to reduced throughput and a higher risk ofparticle formation. It is also known that increased reactiontemperatures can be used to reduce the incorporation of residualammonium chloride. However, this, too, is detrimental as increasedprocessing temperatures reduce the thermal budget available forsubsequent processing and often lead to undesirable dopant diffusion.

For the reasons stated above, and for other reasons stated below whichwill become apparent to those skilled in the art upon reading andunderstanding the present specification, there is a need in the art foralternative methods of chemical vapor deposition.

SUMMARY

The various embodiments of the invention include chemical vapordeposition methods, chemical vapor deposition systems to perform themethods, and apparatus produced by such chemical vapor depositionmethods. The methods involve preheating one or more of the reactantgases used to form a deposited layer. The reactant gases contain atleast one chemical vapor deposition precursor. Heating one or more ofthe reactant gases prior to introduction to the reaction chamber may beused to improve physical characteristics of the resulting depositedlayer, to improve the physical characteristics of the underlyingsubstrate and/or to improve the thermal budget available for subsequentprocessing. One example includes the formation of a titanium nitridelayer with reactant gases containing the precursors of titaniumtetrachloride and ammonia. Preheating the reactant gases containingtitanium tetrachloride and ammonia can reduce ammonium chloride impuritylevels in the resulting titanium nitride layer, thereby reducing oreliminating the need for post-processing to remove the ammonium chlorideimpurity.

For one embodiment, the invention provides a method of depositing alayer of material on a substrate. The method includes heating a reactantgas containing at least one chemical vapor deposition precursor to atemperature within approximately 150° C. of an auto-reaction temperatureof each chemical vapor deposition precursor of the reactant gas,introducing the heated reactant gas to a reaction chamber containing thesubstrate, and reacting the reactant gas in the reaction chamber.Reacting the reactant gas involves reaction of the chemical vapordeposition precursors to deposit the layer of material on the substrate.It is recognized that additional compounds may be incorporated into thelayer of material, such as nonvolatile reaction products from sidereactions deposited in the layer of material as well as volatilereaction products from desired or side reaction products entrapped inthe layer of material.

For another embodiment, the invention provides a method of depositing alayer of material on a substrate. The method includes heating a reactantgas containing at least one chemical vapor deposition precursor to atemperature below an auto-reaction temperature of each chemical vapordeposition precursor of the reactant gas, combining the heated reactantgas and at least one additional reactant gas, introducing the combinedgases to a reaction chamber containing the substrate, and reacting thecombined gases in the reaction chamber. Reacting the combined gasesdeposits at least the layer of material on the substrate. For yetanother embodiment, the additional reactant gases are also heated priorto introduction to the reaction chamber.

For a further embodiment, the invention provides a method of depositinga layer of titanium nitride on a substrate. The method includes heatinga first reactant gas containing titanium tetrachloride to a firsttemperature and heating a second reactant gas containing ammonia to asecond temperature. The first and second temperatures are each below anauto-reaction temperature of titanium tetrachloride and ammonia. Themethod further includes combining the heated first and second reactantgases, introducing the combined first and second reactant gases to areaction chamber containing the substrate, reacting the first and secondreactant gases in the reaction chamber to produce titanium nitride, anddepositing the titanium nitride on the substrate.

For another embodiment, the invention provides a chemical vapordeposition system. The chemical vapor deposition system includes a gassource, a reaction chamber, a gas conduit coupled between the gas sourceand the reaction chamber, a heater, a gas flow temperature sensorcoupled to the gas conduit between the heater and the reaction chamber,and a control system coupled to the gas flow temperature sensor and theheater. The control system is adapted to adjust energy input from theheater to the gas conduit in response to data from the gas flowtemperature sensor. For yet another embodiment, the chemical vapordeposition system further includes a gas flow control valve coupled tothe gas conduit. For this embodiment, the control system is furthercoupled to the gas flow control valve and is further adapted to controlan opening of the gas flow control valve in response to data from thegas flow temperature sensor.

Further embodiments of the invention include deposition methods andchemical vapor deposition systems of varying scope, as well as apparatusmaking use of such deposition methods and chemical vapor depositionsystems.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic block diagram of one embodiment of a chemicalvapor deposition system.

FIG. 2 is an elevation view of one embodiment of a wafer containingsemiconductor dies.

FIG. 3 is a block diagram of one embodiment of an integrated circuitmemory device.

FIG. 4 is a block diagram of one embodiment of an exemplary circuitmodule.

FIG. 5 is a block diagram of one embodiment of an exemplary memorymodule.

FIG. 6 is a block diagram of one embodiment of an exemplary electronicsystem.

FIG. 7 is a block diagram of one embodiment of an exemplary memorysystem.

FIG. 8 is a block diagram of one embodiment of an exemplary computersystem.

DESCRIPTION OF THE EMBODIMENTS

In the following detailed description of the preferred embodiments,reference is made to the accompanying drawings which form a part hereof,and in which is shown by way of illustration specific embodiments inwhich the inventions may be practiced. These embodiments are describedin sufficient detail to enable those skilled in the art to practice theinvention, and it is to be understood that other embodiments may beutilized and that process or mechanical changes may be made withoutdeparting from the scope of the present invention. The terms wafer andsubstrate used in the following description include any basesemiconductor structure. Both are to be understood as includingsilicon-on-sapphire (SOS) technology, silicon-on-insulator (SOI)technology, thin film transistor (TFT) technology, doped and undopedsemiconductors, epitaxial layers of a silicon supported by a basesemiconductor structure, as well as other semiconductor structures wellknown to one skilled in the art. Furthermore, when reference is made toa wafer or substrate in the following description, previous processsteps may have been utilized to form regions/junctions in the basesemiconductor structure, and terms wafer or substrate include theunderlying layers containing such regions/junctions. The followingdetailed description is, therefore, not to be taken in a limiting sense,and the scope of the present invention is defined only by the appendedclaims and equivalents thereof.

FIG. 1 shows a simplified schematic block diagram illustrating oneembodiment of a Chemical Vapor Deposition (CVD) system 100 in accordancewith the invention. It is to be understood that the CVD system 100 hasbeen simplified to illustrate only those aspects of the CVD system 100relevant for a clear understanding of the present invention, whileeliminating, for the purposes of clarity, many of the elements found ina typical CVD system 100. Those of ordinary skill in the art willrecognize that other elements are required, or at least desirable, toproduce an operational CVD system 100. However, because such elementsare well known in the art, and because they do not relate to the designwhich is the subject of the various embodiments, a discussion of suchelements is not provided herein.

The design and construction of CVD systems is well known, and thepresent invention is applicable to any CVD system. The CVD system 100for one embodiment comprises a cold wall reaction chamber 112, typicallyconstructed of stainless steel. The bottom and sides of the reactionchamber 112 may be lined with quartz to protect the walls from filmdeposition during the processing steps. The walls of the reactionchamber 112 may be cooled by a circulating water jacket (not shown) inconjunction with a heat exchanger (not shown). The walls are generallymaintained at or below 100° C., because higher temperatures may inducethe deposition of films on the walls of the reaction chamber 112. Suchdepositions are undesirable because they absorb energy and effect heatdistribution within the reaction chamber 112, causing temperaturegradients which adversely affect the processing steps. Furthermore,depositions on walls may flake and produce particulates that cancontaminate a wafer in the reaction chamber 112. However, such coolingof the walls of the reaction chamber 112 is within the discretion of thedesigner.

A wafer support table 114 or the like is located near the bottom of thereaction chamber 112, and is used for supporting a wafer or substrate116. The support table 114 is generally a flat surface, typically havingthree or more vertical support pins 115 with low thermal mass. Thesupport table 114 may be heated to help reduce temperature variations onthe supported substrate 116.

A wafer handling system 118 is adjacent to the reaction chamber 112, andincludes a wafer cassette 120 and a wafer handler 122. The wafercassette 120 holds a plurality of wafers (substrates 116), and the waferhandler 122 transports one wafer at a time from the wafer cassette 120to the wafer support table 114, and back again. A door 124 isolates thewafer handling system 118 from the reaction chamber 112 when the wafersare not being transported to and from the wafer support table 114.

A showerhead 126 introduces reactant gases 127 into the reaction chamber112, and a plurality of light sources 128 heat the substrate 116. Forthe purposes of this description, the embodiment will be described interms of light sources 128, although other sources of heating asubstrate 116, such as RF and microwave energy, are known and applicableto the present invention. In addition, the showerhead 126 is depicted tobe above the surface of substrate 116, although showerhead 126 mayoptionally be disposed to the side of substrate 116 as well asunderneath substrate 116. Furthermore, distribution devices other thanshowerhead 126 may be used to introduce and distribute reactant gases127 to the reaction chamber 112.

One or more gas sources 130A-B are coupled to the showerhead 126 toprovide one or more of the reactant gases 127 to be disbursed by theshowerhead 126 within the reaction chamber 112. More than one type ofgas may be available from each gas source 130, and reactant gases 127may be provided to the showerhead 126 individually or in combination.

Each reactant gas includes at least one CVD precursor. Examples of CVDprecursors include titanium tetrachloride and ammonia. These precursorscan be combined to deposit titanium nitride. In a pyrolysis system, thereactant gases may require only one CVD precursor. An example of such asystem includes silane (SiH₄) which can be used to deposit silicon (Si)without further precursors. Although the term “reactant gas” is used,one or more of the reactant gases 127 may include a carrier, ornon-reactive, gas. Examples of carrier gases include nitrogen (N₂),argon (Ar), helium (He), and other non-reactive gases used in the art ofchemical vapor deposition. CVD system 100 may further include additionalgas sources providing only carrier gases.

Gas flow control valves 132A and 132B control the flow of gases from gassources 130A and 130B, respectively, through gas conduits 133A and 133B,respectively. Gas conduits represent a flow path for the reactant gases127 between the gas sources 130 and the reaction chamber 112. Gasconduits include such things as piping between elements of the CVDsystem 100 as well as spaces or channels for gas flow within elements ofthe CVD system 100. Gas conduits 133A and 133B merge at combination node135 to become a single gas conduit 137, thus combining the gases fromgas sources 130A and 130B. Gas conduits 133A and 133B can be thought ofas inputs to combination node 135, while gas conduit 137 can be thoughtof as an output of combination node 135. One example of combination node135 includes a simple Y-fitting of piping making up the gas conduits.Another example of combination node 135 includes a gas manifold allowingselection of reactant and carrier gases from a variety of gas sources.Gas conduit 137 may contain a static mixer or other mixing element toimprove homogeneity of the reactant gases 127. For one embodiment, thegas conduits 133A and 133B are not merged outside the reaction chamber.For this embodiment, the gases from gas sources 130A and 130B arecombined subsequent to heating, but within the reaction chamber 112. Oneexample includes a heated showerhead 126 having separate flow channelsfor each reactant gas 127, thus heating the reactant gases 127 prior tocombination in the reaction chamber 112.

Heaters 134A and 134B supply energy to the gas conduits 133A and 133B,respectively, and thus supply energy to the flow of gases from gassources 130A and 130B, respectively. Heaters 134 may be any heater orheat exchanger capable of supplying energy to the gas conduits 133 inorder to produce a rise in temperature to the gases from gas sources130. Supplying energy to the gas conduits 133 may include passingradiation or other energy through the gas conduits 133 that is absorbedby gases within the gas conduits 133. Examples of heaters 134 includeresistive heat tracing, IR radiation sources or other electric heatersas well as direct-fired, jacketed or wrapped heat exchangers. Heatingthus involves raising the gas temperature above an ambient temperature.

Gas flow temperature sensors 136A and 136B sense the temperature of theflow of gases from gas sources 130A and 130B, respectively. For oneembodiment, gas flow temperature sensors 136 sense the temperature ofthe flow of gases directly from the gas flow. For another embodiment,gas flow temperature sensors 136 sense the temperature of one or moreportions of heaters 134 and derive the temperature of the flow of gasesfrom the heater temperatures and the theoretical approach temperaturespredicted by the physical characteristics of the heaters 134, conduits133 and reactions gases 127. For one embodiment, gas flow temperature issensed after combination of the reactant gases 127 in addition to beingsensed prior to combination as depicted in FIG. 1. For a furtherembodiment, gas flow temperature is sensed only after combination of thereactant gases 127.

Jacket 144 may be used downstream of heaters 134 to reduce any tendencyof the gases to condense prior to reaching reaction chamber 112. Jacket144 may be a simple insulative jacket to control energy loss of reactantgases 127 by conduction. Alternatively, jacket 144 may control energyloss by supplying additional energy input to the reactant gases 127, asdescribed with reference to heaters 134, in addition to or in lieu ofproviding insulation. Heaters 134 and jacket 144 may be separate units,as depicted in FIG. 1, or they may be a single unit supplying energy toreactant gases 127 before and after combination. Although not shown inFIG. 1, jacket 144, if not merely an insulative jacket, may be coupledto the control system 146, described below, for control of energy inputby jacket 144. In a similar manner, showerhead 126 may be adapted tosupply energy to the reactant gases 127, as described with reference toheaters 134 and jacket 144, in addition to or in lieu of heaters 134 andjacket 144.

Jacket 144 is coupled to at least gas conduit 137 to control energy lossof reactant gases 127 between combination node 135 and reaction chamber112. As shown in FIG. 1, jacket 144 may be further coupled to at least aportion of gas conduits 133 extending between heaters 134 andcombination node 135.

Exhaust gases are removed from the reaction chamber 112, and a vacuummay be created within the reaction chamber 112, by a gas exhaust andvacuum system 142, as is well known in the art. Also present is a wafertemperature sensor 138, such as a pyrometer, which is used to measurethe temperature of the substrate 116 through a window 140.

A control system 146 monitors and controls the various elements thatmake up the CVD system 100, such as the wafer handler 122, the gas flowcontrol valves 132, the heaters 134, the gas flow temperature sensors136, the wafer temperature sensor 138, and the gas exhaust and vacuumsystem 142. Control system 146 is in communication with the variouselements of CVD system 100 such that process information is passed fromthese elements to control system 146 through communication lines, andprocess control information is passed from control system 146 to variouselements of CVD system 100 through communication lines. It is noted thatcommunications may be bidirectional across a communication line. Controlsystem 146 may include distributed and centralized computerizedindustrial process control systems, as are well known in the art. Suchcontrol systems generally include a machine-readable medium containinginstructions capable of causing the control system, or more directly, aprocessor within the control system, to monitor and control the variouselements coupled to the control system. Examples of suchmachine-readable medium include random access memory (RAM), read onlymemory (ROM), optical storage mediums, magnetic tape drives, andmagnetic disk drives. The machine-readable medium may be fixed, such asan installed hard drive or memory module, or removable, such as amagnetic diskette or data cartridge.

Data indicating the temperature of the substrate 116 is generated by thewafer temperature sensor 138, and is used by the control system 146 toadjust the intensity of the light sources 128 so as to produce a desiredwafer temperature. Data indicating the temperature of the gas flow fromgas sources 130 is generated by the gas flow temperature sensors 136,and is used by the control system 146 to adjust the energy input ofheaters 134, jacket 144 (if not a simple insulative jacket) and/or theflow rate of flow control valves 132 (reductions in flow rate can beused to increase the gas flow temperature at a given energy input).

In addition, multiple wafer temperature sensors 138 may be used to sensethe temperature of different regions of the substrate 116. That data maybe used by the control system 146 to selectively adjust the intensity ofsome of the light sources 128 so as to compensate for uneven heating ofthe substrate 116. The control system 146 also controls when and whatgases are provided to the showerhead 126, as well as when exhaust gasesare removed from the reaction chamber 112, in a known manner.

The operation of the CVD system 100 will be described with reference tothe deposition of titanium nitride (TiN) from titanium tetrachloride(TiCl₄) and ammonia (NH₃). However, the invention is not limited to thischemical system. Other reactant gases may utilized to form layers of TiNas well as layers having other compositions.

For one embodiment, gas source 130A provides titanium tetrachloride andgas source 130B provides ammonia. Flow control valve 132A controls theflow of titanium tetrachloride from gas source 130A as directed bycontrol system 146 in response to a desired titanium nitride depositionrate. Flow control valve 132B controls the flow of ammonia from gassource 130B as directed by control system 146 in response to the desiredtitanium nitride deposition rate. Gas flow may be directly controlled bythe control system 146 by producing a set opening of a flow controlvalve 132 based on a desired deposition rate. Alternatively, gas flowmay be indirectly controlled by the control system 146 by utilizing afeedback controller (not shown) and producing a flow rate setpoint forthe feedback controller which, in turn, controls the opening of a flowcontrol valve 132. Control of gas flows may be responsive to otherfactors in addition to or in lieu of a desired deposition rate. As oneexample, flow of titanium tetrachloride may be responsive to a desireddeposition rate while flow of ammonia may be responsive to a desiredammonia concentration in the reaction chamber 112. To extend thisexample, the flow of ammonia may have a maximum limit such that anammonia concentration calling for ammonia flow rates above the maximumlimit may direct a reduction in titanium tetrachloride flow rate despitebeing lower than expected for the desired deposition rate. As a furtherexample, control of both flow rates may be responsive to desiredconcentrations within the reaction chamber 112.

Energy is supplied by heaters 134A and 134B to the gases from gassources 130A and 130B, respectively, prior to combination of the gasesfor this embodiment. It is generally preferred to heat the gases priorto combination in order to reduce the probability of forming an adductor inclusion complex of the gas molecules. Combining gases cold may leadto formation of an adduct. It is preferred to avoid forming an adduct asthe adduct may require excessive or undesirable energy input to breakthe association of the individual gas molecules. Adducts having anegative effect on deposition may form between a precursor and otherconstituents of the reactant gases, e.g., another precursor or a carriergas.

For one embodiment, one or more of the gases from gas sources 130A and130B are heated to a temperature below the auto-reaction temperature, orthe lowest temperature at which at least one precursor will reactwithout further energy input, prior to introduction to the reactionchamber 112. For another embodiment, the gases from gas sources 130A and130B are each heated to a temperature within approximately 150° C. ofthe auto-reaction temperature prior to introduction. For a furtherembodiment, the gases from gas sources 130A and 130B are each heated toa temperature within approximately 50° C. of the auto-reactiontemperature prior to introduction.

For yet another embodiment, one or more of the gases from gas sources130A and 130B are heated to a temperature at or above which theygenerally will not form an adduct when combined. For a furtherembodiment, the gases from gas sources 130A and 130B are each heated,prior to combination, to a temperature at least approximately 50° C.above the temperature at which they generally will not form an adduct.It is recognized that the auto-reaction temperature and the temperatureabove which the gases will generally not form an adduct are dependentupon the pressure chosen for operation of the CVD system 100.

When only one reactant gas is heated, its temperature should be chosensuch that, when combined with other reactant or carrier gases, no adductwill form and auto-reaction will not occur. While temperaturesapproaching the auto-reaction temperature, and diverging from conditionsfavoring adducts, are preferred, the designer should recognize that hotspots within the heaters may lead to localized reaction if a temperaturetoo close the auto-reaction temperature is chosen.

For one embodiment, the temperature of each reactant gas is adjusted tobe substantially equal at the time of combination. For anotherembodiment, the range of temperatures of the reactant gases has amagnitude of at least approximately 10° C. at the time of combination.When the temperatures of the various reactant gases are notsubstantially equal at the time of combination, temperatures should bechosen such that, when combined, no adduct will form and auto-reactionwill not occur.

For an embodiment utilizing the precursors of titanium tetrachloride andammonia to form titanium nitride, and a CVD system 100 operating at achamber pressure of approximately 0.2-10 torr and a substratetemperature of 450-650° C., the titanium tetrachloride and the ammoniaare each heated to a temperature in the range of approximately 200-300°F. (90-150° C.) prior to combination. Typical flow rates under theseconditions may be 10-50 sccm for titanium tetrachloride and 50-150 sccmfor ammonia. For a specific embodiment, the chamber pressure isapproximately 1 torr, the substrate temperature is approximately 580°C., the titanium tetrachloride flow rate is approximately 30 sccm andthe ammonia flow rate is approximately 100 sccm. It has been reportedthat reaction of titanium tetrachloride and ammonia can be effected attemperatures as low as 200° C. Therefore, the substrate temperaturechosen to drive the reaction at the surface of the substrate should notbe confused with the auto-reaction temperature of the precursors.

For one embodiment, the temperature of the reactant gas containing thetitanium tetrachloride and the temperature of the reactant gascontaining the ammonia are substantially equal at the time ofcombination. For another embodiment, the difference between thetemperature of the reactant gas containing the titanium tetrachlorideand the temperature of the reactant gas containing the ammonia has amagnitude of at least approximately 10° C. at the time of combination.The temperature of the gases before and after combination is maintainedby jacket 144. For one embodiment, the temperature of the gases aftercombination is further raised by jacket 144 in accordance with the aboveguidelines relating to the auto-reaction temperature, i.e., maintainingthe gas temperature below the auto-reaction temperature prior tointroduction to the reaction chamber 112.

The heated reactant gases 127 enter the reaction chamber 112 where theprecursors are transported to the surface of the substrate 116. Thereactant gases 127 react to deposit a layer of material on the surfaceof the substrate 116. In more detail, the precursors of the reactantgases 127 are adsorbed on the surface of the substrate 116 where theyreact and deposit, in this case, titanium nitride. Heating the reactantgases 127 prior to introduction to the reaction chamber 112 as describedabove has been shown to reduce the formation of ammonium chloride indeposited titanium nitride layers, thus reducing or eliminating the needfor an ammonia post-flow procedure. Reducing the formation of impuritiesduring deposition can also permit deposition at reduced chambertemperatures, thus reducing undesirable diffusion within the substrateand improving the thermal budget available for subsequent processing.Accordingly, reactant gas preheating may be used to improve physicalcharacteristics of the resulting deposited layer, to improve thephysical characteristics of the underlying substrate and/or to improvethe thermal budget available for subsequent processing. Furthermore, agiven impurity level may be attained at reduced thermal input to thesubstrate, thus reducing undesirable diffusion of implants in integratedcircuit devices.

As noted previously, and as is well known, integrated circuitfabrication involves the deposition of a plurality of layers supportedby a substrate. The CVD processes and systems described herein may beused to form one or more of these layers. Integrated circuits aretypically repeated multiple times on each substrate. The substrate isfurther processed to separate the integrated circuits into dies as iswell known in the art.

Semiconductor Dies

With reference to FIG. 2, for one embodiment, a semiconductor die 210 isproduced from a wafer 200. A die is an individual pattern, typicallyrectangular, on a substrate that contains circuitry, or integratedcircuit devices, to perform a specific function. At least one of theintegrated circuit devices contains at least one CVD-deposited layerformed in accordance with the invention. For one embodiment, theCVD-deposited layer formed in accordance with the invention is atitanium nitride layer. A semiconductor wafer will typically contain arepeated pattern of such dies containing the same functionality. Die 210may contain circuitry to extend to such complex devices as a monolithicprocessor with multiple functionality. Die 210 is typically packaged ina protective casing (not shown) with leads extending therefrom (notshown) providing access to the circuitry of the die for unilateral orbilateral communication and control.

One example of an integrated circuit device utilizing an embodiment ofthe invention in the formation of various conducting, semiconducting andinsulating layers defining its circuitry is a memory device. As onespecific example, memory devices may include layers of titanium nitrideas diffusion barrier layers in, for example, contacts and wordlines.

Memory Devices

FIG. 3 is a simplified block diagram of a memory device according to oneembodiment of the invention. The memory device 300 includes an array ofmemory cells 302, address decoder 304, row access circuitry 306, columnaccess circuitry 308, control circuitry 310, and Input/Output circuit312. The memory can be coupled to an external microprocessor 314, ormemory controller for memory accessing. The memory receives controlsignals from the processor 314, such as WE*, RAS* and CAS* signals. Thememory is used to store data which is accessed via I/O lines. It will beappreciated by those skilled in the art that additional circuitry andcontrol signals can be provided, and that the memory device of FIG. 3has been simplified to help focus on the invention. The circuitry ofmemory device 300 includes at least one CVD-deposited layer formed inaccordance with the invention. For one embodiment, the CVD-depositedlayer formed in accordance with the invention is a titanium nitridelayer.

It will be understood that the above description of a DRAM (DynamicRandom Access Memory) is intended to provide a general understanding ofthe memory and is not a complete description of all the elements andfeatures of a DRAM. Further, the invention is equally applicable to anysize and type of memory circuit and is not intended to be limited to theDRAM described above. Other alternative types of devices include SRAM(Static Random Access Memory) or Flash memories. Additionally, the DRAMcould be a synchronous DRAM commonly referred to as SGRAM (SynchronousGraphics Random Access Memory), SDRAM (Synchronous Dynamic Random AccessMemory), SDRAM II, and DDR SDRAM (Double Data Rate SDRAM), as well asSynchlink or Rambus DRAMs and other emerging DRAM technologies.

Circuit Modules

As shown in FIG. 4, two or more dies 210 may be combined, with orwithout protective casing, into a circuit module 400 to enhance orextend the functionality of an individual die 210. Circuit module 400may be a combination of dies 210 representing a variety of functions, ora combination of dies 210 containing the same functionality. One or moredies 210 of circuit module 400 contain at least one CVD-deposited layerformed in accordance with the invention. For one embodiment, theCVD-deposited layer formed in accordance with the invention is atitanium nitride layer.

Some examples of a circuit module include memory modules, devicedrivers, power modules, communication modems, processor modules andapplication-specific modules, and may include multilayer, multichipmodules. Circuit module 400 may be a subcomponent of a variety ofelectronic systems, such as a clock, a television, a cell phone, apersonal computer, an automobile, an industrial control system, anaircraft and others. Circuit module 400 will have a variety of leads 410extending therefrom and coupled to the dies 210 providing unilateral orbilateral communication and control.

FIG. 5 shows one embodiment of a circuit module as memory module 500.Memory module 500 contains multiple memory devices 510 contained onsupport 515, the number depending upon the desired bus width and thedesire for parity. Memory module 500 accepts a command signal from anexternal controller (not shown) on a command link 520 and provides fordata input and data output on data links 530. The command link 520 anddata links 530 are connected to leads 540 extending from the support515. Leads 540 are shown for conceptual purposes and are not limited tothe positions shown in FIG. 5.

Electronic Systems

FIG. 6 shows an electronic system 600 containing one or more circuitmodules 400. Electronic system 600 generally contains a user interface610. User interface 610 provides a user of the electronic system 600with some form of control or observation of the results of theelectronic system 600. Some examples of user interface 610 include thekeyboard, pointing device, monitor or printer of a personal computer;the tuning dial, display or speakers of a radio; the ignition switch,gauges or gas pedal of an automobile; and the card reader, keypad,display or currency dispenser of an automated teller machine. Userinterface 610 may further describe access ports provided to electronicsystem 600. Access ports are used to connect an electronic system to themore tangible user interface components previously exemplified. One ormore of the circuit modules 400 may be a processor providing some formof manipulation, control or direction of inputs from or outputs to userinterface 610, or of other information either preprogrammed into, orotherwise provided to, electronic system 600. As will be apparent fromthe lists of examples previously given, electronic system 600 will oftencontain certain mechanical components (not shown) in addition to circuitmodules 400 and user interface 610. It will be appreciated that the oneor more circuit modules 400 in electronic system 600 can be replaced bya single integrated circuit. Furthermore, electronic system 600 may be asubcomponent of a larger electronic system.

FIG. 7 shows one embodiment of an electronic system as memory system700. Memory system 700 contains one or more memory modules 500 and amemory controller 710. Memory controller 710 provides and controls abidirectional interface between memory system 700 and an external systembus 720. Memory system 700 accepts a command signal from the externalbus 720 and relays it to the one or more memory modules 500 on a commandlink 730. Memory system 700 provides for data input and data outputbetween the one or more memory modules 500 and external system bus 720on data links 740.

FIG. 8 shows a further embodiment of an electronic system as a computersystem 800. Computer system 800 contains a processor 810 and a memorysystem 700 housed in a computer unit 805. Computer system 800 is but oneexample of an electronic system containing another electronic system,i.e., memory system 700, as a subcomponent. Computer system 800optionally contains user interface components. Depicted in FIG. 8 are akeyboard 820, a pointing device 830, a monitor 840, a printer 850 and abulk storage device 860. It will be appreciated that other componentsare often associated with computer system 800 such as modems, devicedriver cards, additional storage devices, etc. It will further beappreciated that the processor 810 and memory system 700 of computersystem 800 can be incorporated on a single integrated circuit. Suchsingle package processing units reduce the communication time betweenthe processor and the memory circuit.

Conclusion

Chemical vapor deposition methods utilizing preheating of one or more ofthe reactant gases used to form deposited layers, chemical vapordeposition systems to perform the methods, and apparatus containingdeposited layers produced using the methods have been described herein.The reactant gases include at least one chemical vapor depositionprecursor. Heating one or more of the reactant gases prior tointroduction to the reaction chamber may be used to improve physicalcharacteristics of the resulting deposited layer, to improve thephysical characteristics of the underlying substrate and/or to improvethe thermal budget available for subsequent processing.

One example includes the formation of a titanium nitride layer withreactant gases including the precursors of titanium tetrachloride andammonia. Preheating these reactant gases prior to introduction to thereaction chamber can reduce ammonium chloride levels in the resultingtitanium nitride layer, thereby reducing or eliminating the need forpost-processing to remove the ammonium chloride impurity. Chemical vapordeposition systems as described herein include one or more heaters toraise the temperature of the reactant gases prior to introduction to thereaction chamber.

Although specific embodiments have been illustrated and describedherein, it will be appreciated by those of ordinary skill in the artthat any arrangement which is calculated to achieve the same purpose maybe substituted for the specific embodiments shown. Many adaptations ofthe invention will be apparent to those of ordinary skill in the art.For example, a chemical vapor deposition system may further include aheater for a carrier gas to raise the temperature of the carrier gasprior to combination with a precursor gas or other reactant gas.Furthermore, the heated carrier gas may be combined with a first,unheated, reactant gas, with the heated carrier gas supplying the energyinput necessary to raise the temperature of the combined reactant gas toa desired level in lieu of direct heating of the first reactant gas.Accordingly, this application is intended to cover any adaptations orvariations of the invention. It is manifestly intended that thisinvention be limited only by the following claims and equivalentsthereof.

What is claimed is:
 1. A CVD method of depositing a layer of titaniumnitride material on a substrate, comprising: selecting a reactant gasfrom the group consisting of titanium tetrachloride and ammonia; heatingthe reactant gas to a temperature of approximately 50° C. to 150° C;heating the substrate to at least approximately 450° C. introducing theheated reactant gas to a CVD reaction chamber containing the substrate;and reacting the reactant gas in the reaction chamber, wherein reactingthe reactant gas deposits at least the layer of titanium nitridematerial on the substrate.
 2. The method of claim 1, wherein beating areactant gas comprises heating the reactant gas to a temperature ofapproximately 150° C.
 3. The method of claim 1, wherein the reactant gasfurther comprises at least one carrier gas.
 4. The method of claim 1,wherein reacting the reactant gas further comprises reacting anotherreactant gas.
 5. A method of depositing a layer of titanium nitridematerial on a substrate of a silicon wafer, comprising: selectingreactant gases of titanium tetrachloride and ammonia as chemical vapordeposition precursors; heating one of the reactant gases to atemperature between 90-150° C. to form a heated reactant gas; combiningthe heated reactant gas with the other of the reactant gases in a mixingconduit to form combined gases; introducing the combined gases to a CVDreaction chamber containing the substrate of the silicon wafer hold at atemperature between 450-650° C.; and reacting the combined gases in thereaction chamber, wherein reacting the combined gases deposits at leastthe layer of titanium nitride material on the substrate of the siliconwafer wherein the titanium nitride is substantially free of ammoniumchloride.
 6. The method of claim 5, wherein the other reactant gas isheated to a temperature below 200° C.
 7. The method of claim 5, whereinthe combined gases are further heated prior to introduction to thereaction chamber.
 8. A method of depositing a layer of titanium nitridematerial on a substrate of a silicon wafer, comprising: heating a firstreactant gas containing titanium tetrachloride chemical vapor depositionprecursor to a first temperature between 90-150° C.; heating a secondreactant gas containing ammonia chemical vapor deposition precursor to asecond temperature between 90-150° C., wherein the first and secondtemperatures are within approximately 10° C. of each other; combiningthe heated first and second reactant gases in a mixing manifold prior toentering a CVD reaction chamber; introducing the heated first and secondreactant gases to the CVD reaction chamber containing the substrate ofthe silicon wafer heated to at least 400° C.; and reacting the first andsecond reactant gases in the reaction chamber, wherein reacting thefirst and second reactant gases deposits at least the layer of materialof titanium nitride on the substrate.
 9. The method of claim 8, whereinthe first and second temperatures are substantially equal prior tocombination.
 10. The method of claim 8, wherein the first and secondtemperatures have a difference having a magnitude of approximately 10°C. prior to combination.
 11. The method of claim 8, wherein the firstand second reactant gases each further comprise at least one carriergas.
 12. The method of c claim 8, further comprising heating thecombined first and second reactant gases subsequent to combination andprior to introduction to the reaction chamber.
 13. The method of claim8, wherein the method is performed in the order presented.
 14. A methodof depositing a layer of titanium nitride material on a substrate of asilicon wafer, comprising: heating a first reactant gas containingtitanium tetrachloride chemical vapor deposition precursor to a firsttemperature at approximately 90° C. to 150° C.; heating a secondreactant gas containing ammonia chemical vapor deposition precursor to asecond temperature at approximately 90° C. to 150° C.; combining theheated first and second reactant gases, wherein the combined first andsecond reactant gases have a third temperature between the first andsecond temperatures; heating the combined first and second reactantgases to a fourth temperature below a temperature of approximately 200°C. in a mixing conduit; introducing the combined first and secondreactant gases at the fourth temperature to a CVD reaction chambercontaining the substrate of the silicon wafer heated to approximately580° C.; and reacting the first and second reactant gases in thereaction chamber, wherein reacting the first and second reactant gasesdeposits at least the layer of titanium nitride material on thesubstrate of the silicon wafer wherein the titanium nitride issubstantially free of ammonium chloride.
 15. The method of claim 14,wherein the method is performed in the order presented.
 16. A method ofdepositing a layer of material of titanium nitride on a substrate of asilicon wafer, comprising: heating a first reactant gas containingtitanium tetrachloride chemical vapor deposition precursor to a firsttemperature at approximately 90° C. to 150° C.; combining the heatedfirst reactant gas with a second reactant gas containing ammoniachemical vapor deposition precursor having a second temperature atapproximately 90° C. to 150° C., wherein the combined first and secondreactant gases have a third temperature between the first and secondtemperatures and wherein the third temperature is below approximately200° C.; introducing the combined first and second reactant gases to aCVD reaction chamber containing the substrate; and reacting the firstand second reactant gases in the reaction chamber, wherein reacting thefirst and second reactant gases deposits at least the layer of materialof titanium nitride on the substrate of the silicon wafer wherein thetitanium nitride is substantially free of ammonium chloride.
 17. Themethod of claim 16, wherein the second temperature is approximately 90°C.
 18. A method of depositing a layer of material on a substrate of asilicon wafer, comprising: combining a first reactant gas of titaniumtetrachloride with a second reactant gas of ammonia; heating thecombined first and second reactant gases to a temperature ofapproximately 90-150° C.; introducing the heated first and secondreactant gases to a CVD reaction chamber containing the substrate; andreacting the first and second reactant gases in the reaction chamber,wherein reacting the first and second reactant gases deposits at leastthe layer of material on the substrate.
 19. A method of depositing alayer of titanium nitride on a substrate of a silicon wafer, comprising:heating a first reactant gas containing titanium tetrachloride to afirst temperature of approximately 90-150° C.; heating a second reactantgas containing ammonia to a second temperature of approximately 90-150°C.; combining the heated first and second reactant gases in a heatedmixing manifold; introducing the combined first and second reactantgases to a cold-wall CVD reaction chamber containing the substrate;reacting the first and second reactant gases in the reaction chamber,wherein reacting the first and second reactant gases includes titaniumnitride as a reaction product; and depositing the titanium nitride onthe substrate, thereby forming the layer of titanium nitride.
 20. Themethod of claim 19, wherein the first and second temperatures aresubstantially equal prior to combination.
 21. The method of claim 19,wherein the first and second temperatures, have a difference having amagnitude of at least approximately 10° C. prior to combination.
 22. Themethod of claim 19, wherein the first and second temperatures are eachapproximately 150° C.
 23. The method claim 19, wherein the first andsecond temperatures are each at a temperature above which the titaniumtetrachloride and the ammonia will generally not form an adduct whencombined.
 24. The method of claim 19, wherein the first and secondreactant gases each further comprise at least one carrier gas.
 25. Themethod of claim 19, further comprising heating the combined first andsecond reactant gases subsequent to combination and prior tointroduction to the reaction chamber.
 26. The method of claim 19,wherein the method is performed in the order presented.
 27. A method ofdepositing a layer of titanium nitride on a substrate of a siliconwafer, comprising: heating a first reactant gas containing titaniumtetrachloride to a first temperature of approximately 150° C.; heating asecond reactant gas containing ammonia to a second temperature ofapproximately 150° C.; combining the heated first and second reactantgases in a mixing chamber, wherein the combined first and secondreactant gases have a third temperature of approximately 150° C.;introducing the combined first and second reactant gases to a cold-wallCVD reaction chamber containing the substrate; reacting the first andsecond reactant gases in the reaction chamber, wherein reacting thefirst and second reactant gases includes titanium nitride as a reactionproduct; and depositing the titanium nitride on the substrate, therebyforming the layer of titanium nitride which is substantially free ofammonium chloride.
 28. The method of claim 27, wherein the first andsecond reactant gases each further comprise at least one carrier gas.29. The method of claim 27, further comprising heating the combinedfirst and second reactant gases subsequent to combination and prior tointroduction to the reaction chamber.
 30. The method of 27, wherein themethod is performed in the order presented.
 31. A method of depositing alayer of titanium nitride on a substrate of a silicon wafer, comprising:heating a first reactant gas containing titanium tetrachloride to afirst temperature between 90-150° C.; heating a second reactant gascontaining ammonia to a second temperature between 90-150° C.;introducing the first and second reactant gases to a mixing conduitattached to a CVD reaction chamber containing the substrate; introducingand reacting the first and second reactant gases in the reactionchamber, wherein reacting the first and second reactant gases includestitanium nitride as a reaction product; and depositing the titaniumnitride on the substrate, thereby forming the layer of titanium nitridesubstantially free of ammonium chloride.
 32. The method of claim 31,wherein the method is performed in the order presented.
 33. A method ofdepositing a layer of titanium nitride on a semiconductor substrate, inthe order comprising: cooling the walls of a CVD reaction chamber toless than 100° C.; heating the semiconductor substrate to a reactiontemperature of approximately 580° C.; heating a first reactant gascontaining titanium tetrachloride to a first temperature betweenapproximately 90-150° C.; simultaneously heating a second reactant gascontaining ammonia to a second temperature between approximately 90-150°C., the first and second temperatures being approximately the same;introducing the first and second reactant gases to a heated mixingmanifold prior to introduction into the CVD reaction chamber containingthe semiconductor substrate to produce a heated mixture of reactantgases; maintaining the temperature of the heated mixing manifold atapproximately 200° C.; introducing the heated mixture of reactant gasesto the CVD reaction chamber; reacting the first and second reactantgases in the reaction chamber, wherein reacting the first and secondreactant gases includes titanium nitride as a reaction product; anddepositing the titanium nitride on the semiconductor substrate, therebyforming the layer of titanium nitride.